Most internal combustion engines make use of a circulating liquid to partially remove the heat generated by the combustion process. This liquid is predominantly water that is mixed with glycol-based and/or alcohol-based materials and assorted other compounds. The alcohol and/or glycol-based materials primarily function to raise the water's boiling point and to lower its freezing point. The other added compounds perform ancillary functions such as stabilizing the mixture, inhibiting corrosion and making the fluid easily discernable from water.
A typical antifreeze/water mixture designed for use in an internal combustion engine makes use of an approximately 50--50 mixture of ethylene glycol and water. The resultant mixture will have a boiling point of approximately 235 degrees Fahrenheit and a freezing point of approximately minus 35 degrees Fahrenheit.
The freezing and boiling point temperatures listed in the above example are typical for a relatively unused, freshly mixed quantity of coolant fluid. However, the characteristics of the liquid change significantly over time and with usage in the engine. The alcohols/glycols break down and are converted into related acids such as glycolic acid, oxalic acid and formic acid. This causes a lowering of the fluid's boiling point and a raising of its freezing point. In addition, the acids created by the breakdown of the glycols/alcohols change the ph level of the coolant from approximately 10 (for fresh coolant) down to approximately 7 for old, used coolant.
As the ph level of the coolant decreases, the coolant becomes increasingly corrosive to the exposed metal parts of the engine. Over time, the metal parts become weakened and begin to disintegrate. Also over time, particles of dirt, salt, metal oxides and other metallic and non-metallic particles become entrained or dissolved in the coolant fluid. As an added consequence, some of the particles in the fluid settle on or adhere to the exposed metal surfaces of the engine and effectively reduce the cooling efficiency of the system. In addition, these particles tend to clog small passages in the engine and radiator and thereby cause reduced cooling capacity and create hot spots in the engine. These particles can also build up in the water pump and cause it to fail.
To avoid the above noted problems, replacement of a vehicle's coolant is a routine maintenance procedure that is performed at regular intervals. The old coolant is drained from the engine and replaced with new, fresh coolant. The old coolant is then either disposed of or recycled.
Used engine coolant normally cannot be disposed of by pouring it into a municipality's sewage system. The coolant is toxic and contains dissolved or entrained metals that are not easily broken down. In addition, the glycol and/or alcohol components remaining in solution are still usable and are valuable materials. For these reasons, a concerted effort is being made to recycle the large quantities of used engine coolant that are removed during vehicle maintenance.
The recycling of used engine coolant is normally a complex and expensive process. Miller (U.S. Pat. No. 4,946,595) teaches a typical system for recycling used coolant. He shows a sophisticated apparatus that employs multiple filters and a central tank. A high pressure pump is employed as well as a plurality of valves to control the liquid flow.
All of the recycling equipment presently used for antifreeze is similar to Miller in that the equipment is complex, requires a significant of space, and is extremely expensive to acquire and to operate. It is economically unfeasible for a typical vehicle servicing facility to own such equipment. As a result, antifreeze collected by these facilities is often disposed of and is not recycled. In some cases, the used antifreeze is collected over time until it can be transported to a recycling plant that specializes in the recycling of such fluids. In this latter situation, recycling of the used coolant is extremely inconvenient and is still expensive.